Feedwater heater arrangement for steam turbine power plants



July 7, 1953 J. E. DOWNS 2,644,308

FEEDWATER HEATER, ARRANGEMENT FOR I STEAM TURBINE POWER PLANTS Filed Aug. 21, 1952 450 PSI.

fi/Gl/ P55880195 TURBINE I900 earl. /a

Inverfitor: Jaok )3. Downs,

His Atto rneg.

Patented Jul 7, 1953 r.

FEEDWATER HEATER ARRANGEMENT FOR STEAM TURBmE POWER PLANTS Jack E. Downs, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 21, 1952, Serial No. 305,610

' V {6 Claims. (01. 60-67) v This invention relates to elastic fluid turbine power plants, particularly to'a compound turbine plant with a reheater between turbines, al-

though it may also be used in connection with non-reheat turbines. The characteristic feature resides in a novel feedwater heater arrangement for such power plants.

As the cost of fuel has progressively increased, the manufacturers of large steam turbine power plants have made great efforts to take'full advantage of every smallest possible gain in thermodynamicefiiciency. This has led to a continuous trend towards ever larger power generating units, and, in recent years, increasmg popularity f the so-called' reheat type of compound turbine, in which the motive fluid passes througha high pressure turbine, then is reheated before entering subsequent lower pressure turbines. The present invention relates particularly' to an improved feedwater heater arrangement for such a turbine.

The object of the present invention is to provide an improved feedwater heater arrangement, particularly adapted for a reheat type turbine,

which efiects a small but significant improvement in the overall thermal efiiciency of the power plant.

Other objects and advantages will become apparent from the following description taken in connectionwith the accompanying drawing, in which the single figure represents diagramatically a'steam turbine power plant having a com- 7 pound turbine with a reheater between the high pressure and low pressure turbine'units and an improved multiple feedwater heater arrangement incorporating the invention.

' Generally, the invention is practiced'by providing at least two feedwater heaters in series between the boiler feed pump and the boiler, the

first being heated by steam extracted from the high pressure turbine unit and the second having a special high temperature section arranged to extract a certain increment of thermal energy from the hotter steam extracted from the low pressure turbine. This heat increment is added .to the feedwater discharged from the first heater, and 'servesat the same time to improve the ther mal efliciency of the second heater by reducing .thetemperature differential between the steam and the feedwater being heated by it.

Referring now more particularly to the drawing, the power plant is represented diagrammatically as'comprising a steam generator including a-feedwater pump l supplying preheated .water to a boiler 2 from which highly superheated steam flows through the high pressure turbine 3, a reheater 4, and a low pressure turbine 5. Thev compoundturbine 3, may of 'coursebe arranged in many ways, being represented here as having a common rotor shaft driving a suitable load such as the electrical gen- "9 and a second section II].

The piping circuit interconnecting these components is as follows.

The feedwater pump l receives condensate from the hotwell of a condenser (not shown) or other suitable source in the power plant through conduit II. The feedwater pump discharges through conduit [2 to a set of heat exchange tubes Illa, only one of which is shown in the feedwater heater section Ill. From heater ll], the liquid flows by way of conduit I3 to a set'of tubes la in the primary heater 1. Conduit It connects the heat exchange tubes la with the inlet manifold 9a of the special feedwater heater section 9. The high temperature manifold 90 is connected by conduit with the boiler 2. Conduit l6 admits motive fluid to the high pressure turbine 3. The crossover conduit l'l contains the reheater 4 and leads motive fluid from the exhaust of the high pressure turbine 3 to the inlet of the low pressure turbine 5. Exhaust steam leaves turxbine 5 through an exhaust conduit l8, which may communicate with other still lower pressure tur bines (not shown).

The primary feedwater heater 1 has a special desuperheating section 1b, which may be conveniently formed by a plurality of bafiles 1e arranged to cause the superheated steam to take a serpentine course relative to the heat exchange tubes la, as indicated by the flow arrows in the drawing. The heating steam is admitted to the desuperheating section 7b by conduit l9, which may communicate With the exhaust end of the horizontal legs of the tubes ia. Spent heating fluid from the heater 1 is discharged by way of conduit 20. This spent heating fluid may be further used in other heat exchangers in the power plant (not shown), but it may also conveniently discharge into the high temperature end of the feedwater heater section it, as shown in the drawing.

The secondary heater section i is heated by steam extracted from the low pressure turbine by a conduit 2|. In accordance with the invention, this superheated steam extracted from turbine 5 does not pass directly into the feedwater heater H) but first gives up a certain portion of its thermal energy in the special desuperhea ing section 9. As indicated by the fiow arrows in the drawing, this heating steam flows from the lower end of heat exchanger 9 into' the lefthand end of the feedwater heater section I 0, then takes a serpentine course over the tubes Ella defined by the baffles i021. Spent heating fluid is drained by conduit 22. The remaining thermal energy in this condensate may be utilized in other parts of the power plant, or it may be returned by means of a pump 23 directly into the feed water pump discharge conduit 12.

To render more clear the method of operation, the temperatures and pressures of the feedwater and extraction steam are indicated by legends on the drawing, in degrees Fahrenheit and pounds per square inch, respectively. It will be observed that the secondary feedwater heater section increases the temperature of the feedwater from 330 F. to 370. F., while the primary heater 1 further raises the temperature to 455 F. The special desuperheater section 9 still further increases the feedwater temperature to 464 F.

Attention is particularly directed to the relation between the temperature of the heating steam entering the desuperheater section 9 through conduit 2i and that of the condensate entering the heater 50 through conduit 52. As will be appreciated by those familiar with the thermodynamic theory of such power plants, there is an inherent loss in thermodynamic efficiency in the heat transfer processes occurring in the feedwater heaters i, 8, which less increases as the temperature diflerential between the hotter fluid and the fluid being heated becomes larger. Thus, if the highlysuperheated extraction steam in conduit 2i were discharged directly into the heat exchanger it, the temperature difference between the extraction steam in conduit 2i (at 830 F.) and the liquid in the heat exchange tubes i011 (at well below 400 F.) would involve a substantial inherent thermodynamic loss. On the other hand, with my arrangement, the extraction steam supplied by conduit 2! loses a substantial part of its thermal energy in the desuperheater section 9, and at a smaller temperature differential, so that the heating fluid supplied to exchanger I0 is at a substantially lower temperature (perhaps about 485 F.) more nearly of the same order of magnitude as the highest temperature of the liquid within the tubes llia. Thus, the heat exchange process in heater [0 has a significantly smaller inherent thermodynamic loss.

The importance of this arrangement lies also in the fact that in reheat type turbines the overall plant eiflciency is found to improve as the temperature of the feedwater supplied to the boiler increases for a given reheat pressure. In other words, theaim of the power plant designer is tohave the temperature of the feed water in conduit l5 just as high as possible for a given pressure of the heating fluid extracted through conduit [9, which, in the case illustrated in the drawings, is at the same pressure as the steam at the entrance ii to the reheater 4.

It will thus be apparent that the special heater section 9 increases the overall efficiency of the plant by performing the dual function of (l) effecting a further increase in the temperature of the feedwater supplied to the boiler, and (2) reducing the inherent thermodynamic loss in the feedwater heater it by making the temperature of the heating fluid more nearly of the same order of magnitude as that of the liquid being heated.

Analysis shows that this arrangement may be expected to effect an overall improvement in plant efilciency on the order of .l3%. While this gain seems small, it is of substantial importance in a turbine power plant having an output on the order of 200,000 kw., for an improvement in station efficiency of this order of magnitude may result in a saving of perhaps 600 tons of coal per year. In view of the highly developed state of the modern turbine power plant, and the importance of reducing fuel costs by every possible means, such a saving is of substantial significance to the power plant operator.

While only one form of the invention has been described specifically herein, it will be obvious to those familiar with the art that many changes in arrangement and substitutions of equivalent structures may be made without departing from the invention. As indicated above, the steam extracted through conduit I9 may be derived from an intermediate point in the high pressure tur bine 3, and the spent heating fluid from the primary exchanger '1 may be used in ways other than being discharged into the heat exchanger II? as shown. It will also be understood that a power plant of this type would not ordinarily have only two or three feedwater heaters as described herein, but may have a substantial number of still lower temperature heat exchangers ahead of the feedwater pump I. Also, it is not necessary that the specialheat exchanger 9 be incorporated in the same casing as the secondary feedwater heater It. Thermodynamically the arrangement would be substantially the same if the heater 9 were divorced structurally from the heater I 0; but in many cases it may be more economical to build these two heaters in a common casing, as shown in the drawing. My improved feedwater heater arrangement may be found advantageous in multi-stage turbines other than those having reheaters, in which case it is only necessary that the steam extracted from the turbine for heating the secondary feedwater heater be at a significantly higher temperature :than the feedwater leaving the primary feedwater heater. In such an arrangement the benefits derived would be somewhat less than in a reheat turbine power plant, but might still be worth having.

Many other alterations and substitutions of equivalents will occur to those skilled in the art, and it is of course desired to cover by the appended claims all such changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a steam turbine power plant having a steam generator including a feedwater pump and a boiler supplying motive fluid to a high pressure turbine, a reheater, and a low pressure turbine in series, the combination of a first high temfrom the third heater. 7

2. A steam turbine power plant in accordance with claim 1 in which the first feedwater heater is connected to discharge used heating fluid into the second feedwater heater at a. temperaturesubstantially lower than that of the heating fluid supplied to the third heater and of the same order of magnitude as the temperature of the fluid discharged by the third heater into. the second heater.

,3. In a steam turbine power plant having a .steam generator including a feedwater pump and a boiler supplying motive fluid to a high pressure turbine, a reheater, and a lower pressure turbine in series flow relation, the combination of a primary feedwater heater and a secondary feedwater heater connected in series between .the feedwater pump and boiler, the primary'heater being heated by steam extracted'from the high pressure turbine, the secondary heater including a first section connected in series between the primary heater and the boiler and a second section connected in series between the feedwater pump and the primary heater, the secondary heater being connected to be heated by steam extracted from the lower pressure turbine and flowing through said first section of the secondary heater and then through the second section thereof.

4. In a turbine power plant having a steam generator including a feedwater pump and a 6 heater and the boiler, first conduit means for supplying steam extracted from the low pressure turbine to heat said third feedwater heater, the third heater being connected to discharge heating fluid into said second heater, and second conduit means for supplying spent heating fluid from the first heater to the second heater at a temperature substantially below that of the heating fluid supplied to the third heater and of the same generalorder of magnitude as that ofthe spent heating fluid discharged from the third heater into the second heater.

5. In a steam turbine power plant having a steam generator including a feedwater pump and a boiler supplying motive fluid to a multi-stage turbine, the combination of a first high temperature feedwater heater and a second lower temperature feedwater heater connected in series with the boiler feed pump, and a third feedwater heater connected in series-between said first heater and the boiler, the first heater being connected to be heated by steam extracted from a high pressure point in the turbine, the third heater being connected to be heated by steam extracted from a lower pressure point in the turbine, and the second heater being connected to be heated by fluid discharged from the third heater.

6. In a steam turbine power plant having a steam generator including a feedwater pump and a boiler supplying motive fluid to a multi-stage turbine, the combination of a primary feedwater heater and a secondary feedwater heater,' the primary heater being connected to be heated by steam extracted from a high pressure point in the turbine, the secondary heater including a first section connected in series between the primary heater and the boiler and a second section connected in series between the feedwater pump and the primary heater, the secondary heater being connected to be heated by steam extracted from a lower pressure point in the turbine and flowing through said first section of the secondary heater and then through the second section thereof.

JACK E. DOWNS.

No references cited. 

